In an air duct system, an air flow sensor and control system is used to control the flow of air into a room through supply ducts or out of the room through return or exhaust ducts. Prior air flow sensors include sensors used with a uniform diameter air duct section. When air flow is sensed in a uniform diameter air duct section, the air flow sensor typically has sensor tubes extending across the diameter of the air duct. One of the tubes measures high pressure using upstream openings, and the other sensor tube measures low pressure using downstream openings. The differential between the measured high pressure and the measured low pressure is used to calculate the air flow in the uniform diameter air duct section. See for example Engelke U.S. Pat. No. 4,453,419 and Woodbury U.S. Pat. No. 5,481,925. In commercial embodiments air flow sensors described above have accuracies that is typically no better than 5%. Further, the upstream openings for the high pressure sensor are subject to clogging from lint and other airborne particulate matter.
Another embodiment for measuring air flow employs a Venturi air flow sensor. The Venturi air flow sensor typically has a high pressure section with a diameter that is sized compatibly with the system air ducts and a low pressure center section resulting from a reduced diameter of the Venturi housing. A series of openings are spaced around the high pressure section and are connected to a high pressure tube. Another series of openings are spaced around the low pressure section and are connected to a low pressure tube. The differential pressure between the high pressure tube and the low pressure tube is then used to calculate the air flow through the Venturi. See for example Connet et al. U.S. Pat. No. 1,673,041, Berger U.S. Pat. No. 5,586,861, and Donahue U.S. Pat. No. 9,255,721. Where the pressure sensors are distributed around the perimeter of the Venturi housing, such sensors fail to account for variations in pressure across the diameter of the Venturi housing.